When glass, and more particularly, a windshield is struck by an object or projectile, such as a rock, the outer glass pane is likely to be damaged. As is well known in the prior art, a shatterproof windshield is composed of an intermediate plastic laminate which bonds an outer glass pane and an inner glass pane together. This combination of glass-plastic laminations absorbs the forces of impact, thereby reducing the extent of the damage to the windshield.
Upon impact, glass on the surface of a windshield fractures into a simple crack, or a cone-like formation with damage directed radially therefrom in several directions. When a cone is formed, it normally has a peak on the surface which is often exposed to the atmosphere. The base of the cone typically extends to the bottom of the outer glass pane adjacent the plastic laminate. The sides of this cone, as well as any related fractures that may have formed, are visible to an observer looking through the windshield. Indeed, as light is transmitted through these new interfaces that have formed within the glass, extraneous refraction thereof occurs.
The damage to the windshield, conventionally categorized as a simple crack, a bull's-eye, a star, or a combination thereof, is typically small and confined to the outside glass layer. In the case of bull's-eyes, the fracture planes usually run parallel to the glass surface, sloping downwards. The presence of these fracture planes, which may cover a significant portion of the windshield, can be distracting to the driver and interfere with his line of vision. Furthermore, the presence of fractures, showing as cracks, constitute points of weakness within the outer glass pane. As is well known to those skilled in the art, such cracks are apt to propagate further, resulting in substantial interference with the driver's vision. Accordingly, to avoid a collision caused by such visual distractions and inhibited line of sight, expensive replacement of the windshield is required.
On the other hand, if this damaged glass could have been repaired prior to the propagation of the cracks, by filling the voids within the said damage whereby the fracture planes were properly bonded together, such conventional and costly replacement of the windshield could be avoided.
As is also well known in the prior art, through the use of resins which have refractive indexes substantially the same as that of glass, suitable viscosity, suitable adhesion to glass, and are non-yellowing, it is possible to repair damaged glass and accordingly extend a windshield's life.
Thus, if such resin is injected properly into the damaged glass by one skilled in the art, the interfaces hereinbefore described may be rendered invisible. If such a resin has been applied improperly, however, the damage will still be visible, showing voids, and, of course, have fracture planes that are not bonded together, thereby resulting in cracked glass which is apt to continue to fail.
It is well known to those skilled in the prior art, that filling voids in star damages is difficult, not only because the ends of the star are often far from the point of impact, but also because the passages between the fractured planes are narrow. This damage configuration tends to inhibit or even preclude the flow of a properly injected resin into the damage area.
An alternative method to repair such star damage is to drill holes at these points, to allow for the injection and consequent flow of resin into these locations. Capillary action will then pull the resin into the cracks until opposed by frictional forces. As is known to those skilled in the art, thinning the resin helps delay the affect of these frictional forces upon such capillary action, but this typically causes weak repairs. Accordingly, the repair is ephemeral and only cosmetic.
Many attempts have been made throughout the industry to develop methods and apparatus to enable resin to effectively and reliably penetrate into all voids contained in damaged windshields. Besides drilling holes in the outer glass pane to promote resin flow, the prior art teaches several methods of evacuating air from the damaged area, followed by injecting the resin into the voids, under pressure. Another method known to those skilled in the prior art involves cycles of evacuating and pressurizing.
As will become apparent, those skilled in the windshield repair art have attempted to overcome these and other difficulties associated with filling these voids in damaged windshields. For example, in U.S. Pat. No. 4,597,727, Birkhauser discloses a windshield repair kit which applies a vacuum followed by a pressure cycle to force resin into the voids constituting the damaged area. While the air-evacuation method taught by Birkhauser may be advantageous to repair some damages, it should be apparent that creating a vacuum for each repair is time-consuming and expensive.
It should be clear to those knowledgeable in the art that a repair method using external pressure to cause the penetration of resin into damaged areas, can be advantageous provided an equivalent force is applied on the exterior of the glass surface in an inwards direction against the curvature of the windshield. If this equilibrium is not achieved and maintained during the repair the widening of cracks and the like due to such pressure may cause further failure of the windshield.
In U.S. Pat. No. 3,562,366, Sohl discloses a method of repairing windshields which uses ultrasonic vibration to make the flow of resin into the voids possible.
Werner, in U.S. Pat. No. 3,993,520, discloses a pressure-method followed with vacuum cycles to promote flow of the resin if difficulties are encountered therewith. The Werner windshield repair apparatus consists of a bridge-like member interconnected with two suction cups, which attach to the glass surface. Leveling screws are used to provide support on the opposite side of the injection assembly, in order for it to be in contact with the glass.
When resin is added to the Werner apparatus, pressure is applied, which radiates in all directions. Sideways, the resin is trying to force its way between the seal and the glass surface. However, the same forces provide an uplift on the injection assembly, causing it to move away from the damage. This uplifting action is transmitted to the bridge-like member and suction cups, whereby the bridge is caused to be tilted because of the pivoting effect created where the bridge attaches to the top of the suction cups. As should be apparent, the seal will then become misaligned with the glass surface and the resin will then spill to the outside of the injector. Once this happens, of course, less resin is present in the injection chamber and the necessary pressure is difficult to re-establish.
Accordingly, it should be clear to those skilled in the art that Werner apparatus and method are limited to small damages primarily because it inherently fails to adhere to the glass surface. Thus, while this pressurized injection method has improved the windshield repair art, the problem of how to inexpensively and reliably sustain sufficient downward pressure to secure uninterrupted contact between the seal and the damage has heretofore been unsolved.
As is well known to those familiar with this injection method, filling resin with conventional droppers tends to cause the resin to travel down the inside wall of the injector barrel, thereby coating the threads thereof. Additionally, the vacuum created by unscrewing the injector pin is inadequate to provide the forces to enable trapped air to be expelled from the damage. Since the fracture planes engendered by the cone-shaped damage hereinbefore described are usually sloped relative to the glass surface, such release of the pressure imparted by the injector pin tends to cause air occasionally to float from the damage into the injector.
The pressurized repair techniques known to the prior art are thus limited to repairing relatively small damaged areas, typically in the range of one to one and one-half inches in diameter. As has been explained herein, the voids in windshield damage have narrow passages, and accordingly require high pressures to force resin therein. The repair devices known in the prior art have had limited success providing these prerequisite pressures.
Accordingly, these limitations and disadvantages of the prior art are overcome with the present invention, and improved repair means and techniques are provided which effectively and reliably repair damaged windshields.